Q: Can you help?  My children spotted a wasp flying around in our bathroom tonight, I've never seen a wasp in winter before and don't know where it came from, is this unusual? Mrs G.

A: Dear Mrs G.

 
I presume the wasp was a rather large one - perhaps 2cm long, or a bit more, and about 4 - 5mm rough diameter at the fat part of the abdomen.  And probably a dull yellow and black.  If so, then it was a queen wasp that had awakened from hibernation.  Then they tend to fly fairly sluggishly, although this would get faster if / when the insect warmed up.
 
Guessing that all this fits, then it is not desperately unusual, but certainly a bit early.
 
Queen wasps often over-winter in houses.  They hold on to the back of a curtain with their jaws (or somewhere else a bit tucked away), while they hibernate over the winter period.  (Perhaps for 6 months.)  Then they would naturally come out of hibernation in the spring, as the temperature warmed up, and the days lengthen.  I get lots of them doing this in the loft of my house.  They can even hang onto the fold of a polythene bag.
 
They can sting - although this is probably unlikely if they are not fully alert - semi conscious.
A huge proportion of queen wasps die over winter, and it is believed that only about 0.1%, or less, come through and generate colonies which produce new queens the following year.
 
If you find her again, when she lands on a surface, place an upturned glass over her, then slide a piece of card underneath to enclose her; then lift the glass + card + wasp up - and either let her go outside, or pop it in the freezer to kill her humanely.  Leave her in the freezer for a few hours, then take her out and have a good look at her with a magnifying glass.  Perhaps she could be used for a Show & Tell session at school!